Crude vegetable oils obtained from either pressing or solvent extraction methods are a complex mixture of triacylglycerols, phospholipids, sterols, tocopherols, free fatty acids, trace metals, and other minor compounds. It is desirable to remove the phospholipids, free fatty acids and trace metals in order to produce a quality salad oil with a bland taste, light color, and a long shelf life.
The removal of phospholipids generates almost all of the losses associated with the refining of vegetable oils. As illustrated in FIG. 1, phospholipids contain a phosphate group on one of the two ends of the glycerol backbone, whereas a triacylglycerol contains at least one fatty acid.
The phosphate group of the phospholipid is “hydrophilic” or “water-loving,” meaning that the functional group X is attracted to water. The phospholipid's fatty acid chains R1 and R2 are “lipophilic” or “lipid-loving,” meaning that they are attracted to lipids. Since the phospholipid molecule possesses both a hydrophilic functional group and lipophilic fatty acid chains, it is an excellent natural emulsifier.
The phospholipid's phosphate-containing functional group denoted in FIG. 1 as “X” determines the degree of its hydrophilic nature. The functional group X in FIG. 1 may be any of several of a variety of known types, a few of which are illustrated in FIG. 2.
Phospholipids containing the functional groups -choline and -ethanolamine have the greatest affinity for water, while the acids, acid salts (calcium, magnesium, and iron), and -inositol have much lower affinities for water. Phosphatidic acid and the salts of phosphatidic acid are commonly known as “Non Hydratable Phospholipids” or NHPs. Phospholipids are commonly measured in oil as “phosphorous content” in parts per million. Table 1 contains the typical amounts of phospholipids present in the major oilseed crops, and the distribution of the various functional groups as a percentage of the phospholipids present in the oil.